Marine Reserves and Local Fisheries

An Interactive Simulation

Simulation Exercise

Eugenia Naro-Maciel and Daniel R. Brumbaugh

Center for Biodiversity and Conservation, American Museum of Natural History

New York, 10024, USA

Introduction

In many tropical marine areas such as the Caribbean, one finds productive ecosystems harboring a large diversity of organisms. People also live in these places, and harvest marine organisms for their livelihoods. The complex question arises: How to balance marine biodiversity conservation and local fishery activities? Marine protected areas, including marine reserves that completely ban fishing and other extractive activities, are a promising approach for addressing both of these factors.

This simulation-based exercise is an educational tool that allows users to

1) Explore various factors that influence fish population viability and fishery sustainability; and

2) Experiment with the use of marine reserves as tools in fisheries management.

Highlights

The exercise allows

  • Interactive experimentation by users with marine reserve configurations and species and fishing parameters;
  • Visualization of habitat suitability for three Caribbean fisheries species;
  • Visualization of species abundances and fishing profits over time;
  • Visualization of average harvest catch, effort, profits, and the source of these profits across space; and
  • Saving of all input parameters and simulation results.

Why is this important?

Although the total amount of fisheries catches appears to have a reached a global maximum over the last decade (Watson and Pauly 2001), many local fisheries are known to be declining worldwide. Whereas industrial scale commercial fisheries often switch to new stocks and species after depleting a resource (sometimes leading to a pattern of serial depletions), people in smaller scale, coastal fisheries are much more vulnerable to fisheries collapses. Coral-reef fisheries, due to their relatively small areas, the slow growth and maturation rates of many reef fishes, and the complex community interactions in reef ecosystems, are especially susceptible to overfishing and habitat degradation (Birkeland 2001). Moreover, overexploitation of key reef species has contributed to the instability and decline of coral reefs, leading to threats to the biological diversity of these rich, biodiverse ecosystems (Hughes et al. 2003, Mumby et al. 2006).

Marine protected areas (MPAs), including marine reserves that restrict all take (or harvest), provide tools for addressing threats from overfishing to both the sustainability of local fisheries and the conservation of biodiversity (NRC 2001). A protected area has been defined as an “area of land and/or sea especially dedicated to the protection and maintenance of biological diversity, and of natural and associated cultural resources, and managed through legal or other effective means” (IUCN, 1994). Protected areas, also known as parks, reserves, and by a suite of other names, have been established at international, regional, national, state, and local scales, and many are linked as networks or other systems. Marine resource managers may opt for different combinations of MPA size, number, location, and other factors, depending on the specific objectives of a marine reserve or other MPA. This may include whether, for example, it is primarily designed for conservation or fisheries, for which target species, and in the context of what kind of fishery (e.g., gear type).

This exercise allows users to explore issues related to marine reserves and local fisheries via interactive simulations. Users are able to control (1) some attributes of a local fishery - including population dynamics and mobility of the target species as well as aspects of fisher behavior and economic factors, and (2) the extent and placement of marine reserves. By exploring the contributions of these issues to fisheries productivity over time, users should gain some understanding of the factors contributing to how reserves can interact with local fisheries. Of course, although many of the factors and dynamics in this exercise are based on actual interdisciplinary research conducted in The Bahamas (see the simulation represents a simplification of the real complexities of population dynamics, fisheries economics, and marine resource management. Adding these additional complexities, such as more variable population dynamics, more dynamic pricing of catches, and additional fishing regulations outside of marine reserves, would likely lead to different quantitative outcomes. Nevertheless, qualitative results deriving from controlled comparisons across different scenarios (e.g., species life-history, fleet, and reserve characteristics) are likely to be more general.

Local fisheries

In the Caribbean, three important fisheries species, for economic, cultural, and ecological reasons, are the queen conch (Strombus gigas), the Nassau grouper (Epinephelus striatus), and the spiny lobster (Panulirus argus).

Queen Conch

The queen conch, a large snail (gastropod mollusk) in the Strombidae family, is found throughout and beyond the greater Caribbean, including as far north as Bermuda and as far south as Venezuela and Brazil (FAO 1977). The conch fishery is one of the most important in the region, though the species’ biology makes it rather susceptible to overfishing, and it has declined throughout its range in recent decades. Trade in queen conch is now restricted following regulations of the Convention on International Trade of Endangered Species of Wild Fauna and Flora (CITES), where S. gigas is listed on Appendix II (CITES undated, Acosta 2006). The species is also listed in Annex III of the Protocol Concerning Specially Protected Areas and Wildlife to the Convention for the Protection and Development of the Marine Environment of the Wider Caribbean Region (SPAW, UNEP undated).

Economically, the conch fishery in the Caribbean is worth millions of U.S. dollars each year. Although harvest dates to prehistoric times, high levels of commercial take are relatively recent. The meat can be prepared in a variety of ways (e.g., raw ceviche-type salad, stews and chowder, or cooked in innumerable customary ways), while shells are used to make jewelry, and as a local construction material. Fishing methods include capture by hand, use of simple gear such as forked poles, or SCUBA, which is generally illegal (Catarci 2004). These methods do not greatly negatively affect habitats or ecosystems, or other species through incidental by-catch (Cascorbi 2004). In some areas, like The Bahamas, conch is harvested during the lobster fishery closed season, or as part of a multiple species effort (Catarci 2004). Management is coordinated regionally by the International Queen Conch Initiative. The fishery is regulated through temporal or spatial closures, as well as by level of maturity, size limits, gear restrictions, and catch quotas. Conch fishing in Florida – both commercial and recreational – has been prohibited since 1985, though stocks have not recovered subsequently. In 1991, the state recognized S. gigas as a “protected species” (Schlesinger 2006). In many nations, fisheries management measures are not effective due to factors such as illegal fishing and inadequate enforcement (Cascorbi 2004, Acosta 2006).

Aspects of this species’ biology contribute to its vulnerability to overharvest (Gascoigne 2002, Gascoigne and Lipcius 2004, Cascorbi 2004). Queen conchs are relatively long-lived, slow growing, have delayed sexual reproduction, with a reproductive output that increases with age (CHC CIC 2003). S. gigas live up to about 25 years, mature at around 3-4 years, and are highly fecund. Reproduction occurs through internal fertilization, when large numbers of conch migrate to shallow waters for breeding. Females lay individual masses containing ~300,000 fertilized eggs. After about 5 days, larvae called veligers hatch from these egg masses and start a 3-4 week period in the plankton before settling onto shallow sand and algae, where they metamorphose into tiny snails. The conch’s life history is characterized by high mortality at younger ages, however older individuals are naturally protected from predators by their strong shells. This species is, however, relatively easy for humans to capture. It lives in accessible shallow waters, is clearly visible, and moves slowly. S. gigas occur mainly in shallow sea grass beds linked to coral reefs, with the youngest being found closest to shore. Queen conch forage on plankton as larvae, and algae, sea grass, and other plants as adults (Ray and Stoner 1995, CHN CIC 2003). Vulnerability increases when conch aggregate in large numbers to spawn. This anthropogenic mortality of the later life stages, combined with habitat loss and pollution, are likely to be driving population declines. Further, reproduction in S. gigas may fail below certain density thresholds, inhibiting recovery (Stoner and Ray-Culp 2000, Gascoigne and Lipcius 2004).

Nassau Grouper

The Nassau grouper, Epinephelus striatus, a member of the sea bass family (Serranidae), was historically found throughout the tropical western Atlantic Ocean, including the Caribbean Sea, the Gulf of Mexico, the southeastern U.S., Bermuda, and northern South America (Sadovy and Eklund 1999). Currently, this species occupies only a fraction of its previous range, and is classified as Endangered according to the World Conservation Union (IUCN 2006). Under this definition, endangered taxa are those that have suffered a high rate of population decline and are at risk of extinction; E. striatus has declined by about 60% over the last three decades (IUCN 2006). Historically, the grouper fishery has been one of the most important and valuable throughout its range (Sadovy and Eklund 1999, Gascoigne 2002). Grouper is used in traditional dishes, such as boiled fish and grouper fingers, where it is valued for having relatively few bones and being easy to eat. In The Bahamas, one of the few countries where stocks remain commercially viable (though much less abundant than in previous decades) and whose capital is the namesake of the fish, Nassau grouper has been the most valuable finfish in recent years. Commercial landings there were valued at over BSD$ 2.7 million in 2003 (Department of Fisheries [now, Marine Resources], The Bahamas undated).

Nassau grouper grow slowly and have delayed reproduction, reaching sexual maturity from 4-8 years of age when they reach 40-50 cm in length (Ray and McCormick-Ray 2004). These characteristics hinder population recovery from low densities, enhancing vulnerability to overfishing. These groupers are long-lived, capable of surviving over 20 years in the wild, and have naturally low adult mortality (Sadovy and Eklund 1999). Reproductive rate and number of eggs per reproductive event increase with age in this species, with large fish producing 5-6 million eggs per season. Most groupers change sexes with age, although this may not be the case for E. striatus. Fishing often targets larger individuals, eliminating those with highest reproductive capacity and skewing the age class distribution to juveniles with lower survivorship (Gascoigne 2002). During the winter months (e.g., November to February in The Bahamas, and December to March in Belize), adults undergo breeding migrations to specific offshore areas, either locally or up to hundreds of kilometers away from their resident habitats, where they form ephemeral spawning aggregations during the week around the full moon (Starr et al. 2007). These groups, historically numbering in the tens of thousands, form for reproductive and courtship purposes (Sadovy and Eklund 1999). Because there aggregations are predictable and often known to local fishermen, large numbers of fish can be readily caught during spawning. Uncontrolled exploitation has completely extirpated or reduced many spawning aggregations to a few dozens to thousands of fish, rendering many stocks commercially extinct, and disrupting spawning behavior (Sala et al. 2001, Gascoigne 2002, Sadovy 2002, Ray and McCormick-Ray 2004, Sadovy and Domeier 2005). Once eliminated, spawning aggregations have not been observed to form again, suggesting that knowledge of spawning sites depends on cultural transmission (Bolden 1980). Young groupers, in the absence of enough older, reproductively experienced individuals, seem unable to locate their spawning site. As a consequence, small aggregations with too few experienced individuals to facilitate enough new recruits to the aggregation may be doomed to extinction (Sadovy and Eklund 1999, Starr et al. 2007).

Measures have been instituted to limit fisheries in response to the observed decline in grouper numbers. These include seasonal closures (e.g., during the winter spawning months) and spatial closures around known spawning sites. In place also are gear restrictions and harvest limits for fish size and number. Commonly employed fishing methods include handline, traps, and spear guns. Marine protected areas have been hailed as one of the most promising methods for protecting Nassau Grouper (Sadovy and Eklund 1999, Gascoigne 2002). Taxation based on vessel or harvesting characteristics is another possible alternative measure.

Habitat use, diet, and ecological role vary throughout the grouper life cycle (Sadovy and Eklund 1999, Perry Institute undated). Larvae hatch from pelagic eggs within a day after fertilization. After about 30–50 days, small juveniles leave the water column, shifting to inshore benthic nursery areas such as algal beds, seagrass, or reefs, where they will start life as relatively sedentary, demersal organisms. As they grow, they gradually shift their residences, to deeper reef habitats containing adequately sized holes, cracks, and other concavities (Ray and McCormick-Ray 2004). As adults, with the exception of the annual breeding migrations, Nassau grouper rarely disperse from their territories. They also shift their diets as they age, with juveniles feeding mainly on crustaceans, and adults feeding on a mix of invertebrates and fishes. Nassau grouper are among the larger reef fish, reaching up to 120 cm (3.9 feet) in length and approximately 25 kg (55 lbs.) in weight (Ray and McCormick-Ray 2004). A predator whose diet includes crustaceans, reef fishes, and octopuses, E. striatus plays a key role in reef communities (Mumby et al. 2006). Throughout its life cycle, this species also serves as prey for reef sharks, barracuda, dolphins, and humans. In addition, as with other reef fishes, E. striatus acts in a suite of symbiotic relationships, visiting cleaning stations, for example, where various species of small fishes (especially certain wrasses and gobies) or shrimps remove parasites from their exterior and inside their mouths. Thus, Nassau groupers are functionally linked to reef communities in numerous ways, and decreases in their populations will have community-wide impacts.

Spiny Lobster

The Caribbean spiny lobster (Panulirus argus), found in the Gulf of Mexico, the Caribbean Sea, and the Western Atlantic Ocean from North Carolina, U.S.A., to Rio de Janeiro, Brazil (FAO 2004), is a member of the ecologically and economically important rock or spiny lobster family, Panuliridae. Apart from the supporting lucrative commercial and recreational fisheries, these gregarious crustaceans are known for their migratory behavior, which can involve single-file group movements of juveniles and adults from shallow to deeper waters, related to seasonal, severe weather, or other factors (Herrnkind et al. undated). Larvae often disperse across national territories, so that management in one country may affect populations in others. This arthropod is omnivorous, scavenging mainly nocturnally on diverse kinds of plant and animal matter, including crustaceans and mollusks (Bliss 1982, Briones-Fourzan et al. 2003). Lobsters, in turn, are prey for various organisms, including sharks, groupers, snappers, sea turtles, octopuses, and humans.

Spiny lobsters, commonly known as crawfish, are harvested throughout their range. This multi-million dollar fishery is one of the most valuable in the Caribbean (Cascorbi 2004, Bene and Tewfik 2001). Capture methods include free diving, use of traps, spears, and trawls (Bene and Tewfik 2001, FAO 2004). Spiny lobster fisheries in Florida and The Bahamas are intense, but do not result in notable harm to habitats and ecosystems, and levels of by-catch are low (Davis 1977, Davis and Dodrill 1989, Eggleston et al. 2003, Cascorbi 2004). In some areas, such as the Turks and Caicos, Panulirus argus may be harvested jointly with the Queen Conch (Bene and Tewfik 2001). Caribbean spiny lobsters are not classified as endangered or threatened, although they are listed on the SPAW protocol (UNEP undated). Aspects of their biology, such as rapid growth, a relatively early age of sexual maturity, high reproductive potential, and the potential for long-distance dispersal may contribute to a relatively low susceptibility to extirpation from overfishing (Cascorbi 2004). Fisheries are regulated, including measures such as closures during spawning season, trap-reduction programs and legal size and bag limits. Also illegal in some countries is harvesting of egg-bearing females, and fishing with firearms or explosives. Effectiveness of enforcement varies regionally (Cascorbi 2004). Marine reserves protect lobsters and their habitats, although very small protected areas may be inadequate (Eggleston and Dahlgren 2001).

Spiny lobsters occupy a variety of environments throughout their life cycle, which spans up to 30 years. Reproduction and fertilization occur in offshore reef areas, generally during late spring or early summer. During the mating process, males deposit a sticky fluid containing sperm onto the female’s abdomen; this fertilizes the eggs upon release (Herrnkind et al. undated, Bliss 1982). Fertilized eggs remain under the female’s tail until they hatch, and clutch size varies with location and fishing pressure. In the Dry Tortugas, for example, lobsters became reproductively active at larger sizes, and the average number of eggs is higher than in a south Florida fishery (Bertelsen and Matthews 2001). Eggs hatch into transparent phyllosome larvae that drift offshore with the surface currents. This pelagic stage generally lasts 6-12 months, resulting in long distance dispersal spanning hundreds of kilometers (Herrnkind et al. undated). They next molt into free-swimming puerulus postlarvae, which leave the open ocean to settle in nearshore vegetated benthic areas such as sea grasses, algal beds, or mangroves (Acosta et al. 1997, Acosta 1999, Butler et al. 1997). This process is thought to vary with characteristics of the nursery habitat, postlarval supply, environmental factors, fishing pressure, and oceanographic circulation (Lipcius et al. 1997, Butler et al. 2001, 1997, Cruz et al. 2001, Lipcius et al. 2001, Yeung et al. 2001). Postlarvae metamorphose into juveniles, whose movements are asocial and initially restricted to sheltered areas such as algal beds (Butler et al. 1997, Herrnkind et al. undated). As time goes on they become increasingly vagile and social, living in small aggregations inside crevices, under rocks, seaweeds, sponges and corals (Eggleston and Dahlgren 2001). As lobsters approach maturity, which may occur around 2-3 years of age, they move to deeper waters in coral reef systems where reproduction occurs (Herrnkind et al. undated).